In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In the third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, with the UMTS network, successor systems of LTE are also under study for the purpose of achieving further broadbandization and higher speed (for example, “LTE-advanced” (LTE-A)).
This LTE-A system provides for multiple-user MIMO (MU-MIMO) transmission to transmit transmission information sequences from different transmitting antennas to different users at the same time. In MU-MIMO transmission, it is possible to transmit data for a plurality of user terminal UEs in the same time and the same frequency. When allocating downlink control information for many user terminal UEs to a PDCCH region, cases might occur where the PDCCH region to transmit downlink control information runs short. In this case, the number of user terminal UEs that can be multiplexed over the PDSCH region is limited. As a method of solving such shortage of the PDCCH region, it may be possible to extend the PDCCH allocation region beyond the control region of maximum three OFDM symbols from the subframe top (that is, extend the PDCCH region into the conventional PDSCH region) (enhanced PDCCH).